The volumetric swelling ratios of three coals and their maceral concentrates in the presence of pyridine were determined by the displacement of a piston and by the measurement of swollen and unswollen particle size distributions using a laser diffraction particle size instrument. The use of particle size distributions allows the measurement of swelling ratios without the possible problems of changes in particle packing associated with the piston apparatus. The piston apparatus, however, has the advantage that the kinetics of solvent uptake can be evaluated. Equilibrium swelling ratios were generally found to increase in the order vitrinite > liptinite > inertinite, which implies that the apparent cross-link density increases in the order inertinite > liptinite > vitrinite. Extracted coals and maceral concentrates were found to have greater swelling ratios than raw coal samples.